The present invention is directed to a method for drawing cables which inherently do not have tensile strength, particularly light waveguide cables, into cable channels or cable pipes. The invention is also directed to the application of this method for connecting a cable at a terminal tower to an exchange via an overhead line.
Dependent on the conditions of stress to which the cables are subjected in the field, light waveguide cables and electrical cables as well are either an armored and/or tensile cable or a lightly built cable having a low tensile strength. The cables with low tensile strength are employed when the cables can be combined and used with another cable, for example a carrying cable.
Armored and/or tensile cables have the required tensile strength, so that they can be drawn into cable channels or pipes. One application of such a cable is the connection of a light waveguide cable incoming at a terminal tower of an overhead line to an exchange arranged at the terminal tower. The cable is thereby usually pulled through the cable channels or pipes, so that it must have a tensile strength that is adequate for this assembly purpose.
One example of light waveguide cables or LWG cables which do not have tensile strength in and of themselves is what is referred to as an LWG shackle cable. An LWG shackle cable usually is about 5 mm thick and is an all dielectric-like waveguide cable or AD-LWG cable that can be shackled to a guard wire or phase wire of an overhead line by a shackle band. The shackle band is wrapped around both the guard wire as well as around the light waveguide cable. Obviously, the light waveguide cable does not require any particular tensile strength for this application.
In practice, however, there are cases wherein one can manage with a lightly constructed, unarmored cable over by far the greater part of a distance that must be bridged by the cable. The cable that has an adequate tensile strength is needed on short intermediate or final paths. In these instances, the cables were previously cut off and a tensile cable was attached with the assistance of a fitting. After bridging the distance that required the tensile cable, a switch was made back to the inherently non-tensile strength cable via fitting. This is more economical than using an armored or tensile cable for the entire length of the cable, because of the lighter structure.
An example of such a situation is the connection of an AD-LWG cable that arrives at a terminal tower of an overhead line and is connected to an exchange. Up to now, the cable ends of the AD-LWG cable were guided into a fitting at a terminal tower, and an armored and/or tensile cable leads into the exchange therefrom, whereby the length of this connection usually amounts to between 10 m to 300 m. Specific, expensive, short cable lengths must then be fabricated for this connection between terminal tower and exchange, and this is expensive and involved because it is always only short pieces that can or must be produced. On the other hand, the lack of tensile strength on the part of the AD-LWG cable does not allow this cable to be drawn directly through cable channels or pipes from the terminal tower up to the exchange.
The invention is based on the object of offering a method for drawing cables which do not have tensile strength in and of themselves into cable channels or cable pipes and an application of this method to the connection between terminal towers and exchanges that makes the fabrication of specific, expensive, short lengths of armored cable for short distance connections of this type unnecessary.
To accomplish this object, the method is directed to providing a tensile yarn skin to an end of the cable, and then drawing the end of the cable having the tensile yarn skin into a cable channel or cable pipe. The connecting cable incoming at a terminal tower to a switching center can be connected to a cable having the yarn skin, which is applied for the distance that is necessary for being pulled through the various channels or cable pipes.
In accordance with the present invention, a method for drawing cables that inherently have no tensile strength, particularly LWG cables, into cable channels or cable pipes is characterized in that the cable is provided with a tensile yarn skin before being drawn into the pipe or channel. The cable that is unsuitable for higher drawing forces is strengthened by applying the tensile yarn skin so that the cable can be pulled through cable channels or cable pipes from the terminal tower without having to employ special cables for this purpose. It has been shown that a simple tensile yarn skin suffices for this specific purpose, which is the pulling of the cable through a cable channel or a cable pipe over a short distance for a single time.
An advantageous development of the invention is that the tensile yarn skin is applied at the assembly location. It becomes possible to strengthen the incoming cable and introduce it into the cable channel or pipe without interruption and interposition of a fitting.
An advantageous development of the invention is that the net hose is pulled onto the cable as the tensile yarn skin. This yarn skin can be advantageously implemented by a simple mechanism without rotating parts, whereby the supply of the net hose in the mechanism is adequate for the short lengths that are planned.
Another advantageous development of the invention is that an annular receptacle device is employed for a net hose supply. The cable is pulled through the receptacle device and the net hose is thereby taken down from the receptacle device and pulled onto the cable. The cable can, thus, be strengthened in a simple way, and it is advantageously possible to always keep the required supply of net hose on hand for the cable lengths to be fabricated.
Another advantageous development of the invention is that a yarn is spun around the cable as a tensile yarn skin. By applying spinning technology, it is advantageously no longer necessary to set the supply of material for the yarn skin to the cable length to be strengthened, since the spin-wrap can be ended at any time.
Another advantageous development of the invention is that a known yarn spinner or yarn twister is employed for the spin-wrapping of the cable. This is a proven technology that meets the task envisioned here.
Another advantageous development of the invention is that the net hose or, respectively, spin-wrap is fixed by a tensile cable cap at the end of the cable. What is thereby advantageously achieved is that the yarn skin fulfills its purpose when the cable is drawn in and does not slip off from the cable.
Another advantageous development of the invention is that a fiber selected from Kevlar fibers and glass fibers are employed as the yarn skin. It is thereby advantageously a matter of fibers that produce the desired tensile strength without further ado.
The solution of the task also comprises the application of the above-characterized method for connecting a cable incoming at a terminal tower to a switching center or exchange. Here, the yarn skin is applied on this distance between the tower and center. This application is especially advantageous insofar as expensive, short lengths of armored and/or tensile cable have had to be previously employed in this application.
Another advantageous development of the above-mentioned method is that the cable is conducted down from the terminal tower, strengthened and pulled in without interruption or use of any fitting. This solution is advantageous when the distance between the terminal tower and the exchange is comparatively short, so that the cable coming from the terminal tower can be laid in a ring, strengthened and then drawn into the exchange.
Another advantageous development of the above-mentioned application is that the cable incoming at the terminal tower is guided into a fitting and connected to a cable of the same type that is reinforced with the tensile yarn skin and is kept on hand on a cable drum. The connection in the fitting occurs after the reinforced cable is drawn into the cable channel or cable pipe. This solution is advantageous when the distance between the terminal tower and the exchange is greater because practically any arbitrary length for the reinforced cable is then available on the cable drum for the connection between the terminal tower and the exchange. The subsequent connection of the strengthened cable with the fitting at the terminal tower is advantageous because the short length net hose need not be unwound in advance in this case before it is drawn into the cable channel or pipe.
Finally, another advantageous development of the invention is characterized in that the light waveguide shackle cable is employed as the cable. When laying such a cable, the inventive method is especially advantageous with respect to handling and cost savings.
Other advantages and features of the invention will be readily apparent from the following description of the preferred embodiments, the drawings and claims.